operation. In large laboratories vacuum-pans are employed to remove the atmospheric pressure, enabling the evaporation to be accomplished at a much less degree of heat than if the liquid were exposed to the air. Ebullition or Boiling is a form of evaporation.

SPONTANEOUS EVAPORATION is the evaporation of a liquid without the direct application of strong heat, but at the temperature of the room or closet used for the purpose. It is especially applicable to cases in which the residue is liable to injury or loss from much heat, or to secure finer crystals than can be obtained by quick evaporation of their solution.

Distillation consists of two processes, (1) the evaporation of a liquid, (2) the condensation of the vapor into a liquid in a separate vessel. The agent used in the first part of the operation is heat, in the second part cold. Its object is to separate mixed volatile and fixed substances, or to combine volatile substances which cannot otherwise be mixed, as in the preparation of some of the official Waters. The apparatus used is of great variety, from the simple retort and receiver to the elaborate and costly stills.

DESTRUCTIVE OR DRY DISTILLATION is a process of decomposing an organic substance by heat into volatile products which are collected in a separate vessel, the residue being said to be carbonized. It is only employed by large manufacturers, for the preparation of Acetic and Succinic Acids, Oil of Amber, Wood-tar, etc.

FRACTIONAL DISTILLATION is the separation by distillation of substances which are volatile at different temperatures, each being separately driven over and received in a vessel by itself. Different degrees of heat are successively employed in accordance with the volatilizing points of the substances to be obtained.

Sublimation is the distillation of a volatile solid, the product being termed a sublimate. Its objects are to purify volatile solids from impurities, and to collect such as result from chemical action at high temperatures. The operation is carried on in iron, glass or stoneware retorts, and results in cake sublimates or powder sublimates according as the temperature of the condensing surface is high or low.

Roots, leaves and seeds are

Desiccation is the process of removing moisture from solids, and has for its object either the preservation of the substance, the reduction of its bulk or the facilitation of its comminution. The operation should be conducted at as low a temperature as possible. generally dried by being placed in trays of wire net-work and exposed to a uniform temperature in a room heated by steam. A better method is to suspend organic substances from the ceiling of an attic during warm weather; a slow process, but one which does not result in much loss of the active volatile principles. Crsytals and precipitates require a higher temperature and are usually dried on a water-bath. When the water of crystallization is to be expelled, as in desiccating Alum and Sulphate of Iron, a temperature of about 400° F. is required. In absorbing water from alcohol Carbonate of Potassium and slaked Lime heated are employed, and in several instances Sulphuric Acid is the desiccator used.

Fusion is the process of liquefying solids by the application of high. heat without the use of a solvent. It is employed in making ointments, plasters, etc., in purifying resins, and for the purpose of decomposition. The degree of heat required varies from a temperature of 90° F., sufficient to melt lard in an open vessel, to one of 800° F., employed in fusing Zinc in an earthen crucible; and may be regulated by the aid of the water-, steam- or sand-bath. The two former appliances limit the degree of heat applied, while the sand-bath prevents sudden changes in the temperature. Oil-baths and glycerin baths are employed in fractional distillation on a large scale.

Exsiccation or Calcination is the process of depriving a solid of its moisture or other volatile constituents by the application of heat without fusion. The term Exsiccation is usually applied to the vaporization of the water of crystallization from a crystalline body, Calcination, to such operations as the expulsion of carbonic acid and water from carbonates, as in the manufacture of Lime, Magnesia, etc.

Carbonization is the heating of organic substances without exposure to the air until the volatile constituents are driven off, and the residue assumes the characteristic appearance of carbon.

Incineration is the heating of organic substances with access of air until the carbon is consumed, the ashes remaining being the product desired.

Ignition in pharmacy means the process of strongly heating solids or semi-solid substances, the residue left being the product desired. It is used in the official quantitative tests for Phosphoric Acid, Phosphate of Ammonium and purified Sulphide of Antimony.

Deflagration is the heating of an inorganic substance with another which yields oxygen (usually a nitrate or a chlorate), the result being the decomposition of the body, with violent and sudden combustion.

Torrefaction or Roasting is, the application of heat, in a less degree than for carbonization, to an organic substance for the purpose of modifying some of its constituents, as in the roasting of coffee and rhubarb. The latter substance when subjected to this process, loses its cathartic properties but retains its astringency, and is known as Torrefied Rhubarb.

Comminution is the process by which the aggregation of the particles of a solid body is overcome, and the body is reduced to pieces of varying sizes. Its object is to increase the surface exposed to the action of solvents, and it includes the mechanical operations of cutting, rasping, grating, crushing, stamping, grinding, pulverizing, triturating, levigating,

OFFICIAL OPERATIONS.

421 elutriating, granulating, etc. Apparatus of various kinds, as cutters, mortars and pestles, mills, etc., are used for the comminution, while spatulas are employed to loosen the particles, and sieves to sift the coarser from the finer. These last-named contrivances are of five sizes, designated by the number of their meshes to the inch, 80, 60, 50, 40 and 20, respectively permitting the passage of powders termed very fine, fine, moderately fine, moderately coarse and coarse.

Trituration is the comminution of a solid to an extremely fine powder by continued rubbing in a wedgewood mortar with an inert and gritty powder, Sugar of Milk being the substance directed to be used. The product is called a Trituration (see that title under OFFICIAL PREPARATIONS). The surfaces of the mortar and pestle-head should coincide closely, and the thorough comminution of the trituration is best accomplished by a circular motion of the pestle in gradually increasing circles, until the side of the mortar is reached, then reversing the motion, and gradually lessening the circles until the pestle reaches the centre again. The process is greatly facilitated by having the pestle attached to a long handle playing in an opening made in a piece of wood which is nailed at a convenient height. A weight may be fixed on top of the handle if a greater degree of friction be desired.

PULVERIZATION BY INTERVENTION is only another name for trituration when performed in a mortar and with solid bodies, the foreign substance used being subsequently removed. Potassium Sulphate may be employed as the medium for the pulverization of Gold, and is then dissolved out with water. Alcohol or Chloroform may be added to Camphor to aid its pulverization, and then removed by evaporation. Phosphorus may be pulverized by placing it in water, gently heating the latter until the phosphorus is melted, and agitating the whole while cooling.

LEVIGATION is trituration of a substance made into paste with water or some other liquid, and resembles the old process of grinding oil paints by hand on a slab of stone. The process is used for coarse materials, as chalk, etc., where the refuse is rejected, or for such substances as Red Oxide of Mercury, Oxide of Zinc, etc. When performed with a porphyry slab and muller it is termed Porphyrization.

ELUTRIATION is a water-sifting process for separating the coarser particles of insoluble substances from the finer. The substance is mixed with water and after the larger particles have fallen to the bottom, the liquid is decanted into another vessel, in which the light and powdery particles are collected.

Solution is the dissolving of a solid or a gaseous substance in a liquid, and may be simple when the substance undergoes no alteration, being recovered unchanged on evaporation, or chemical, when the dissolved body is chemically altered by the solvent of some other substance present, and cannot be recovered on evaporation. Simple Syrup is an instance of simple solution, the Syrup of Lime one of chemical solution. The liquid employed is termed a solvent before the substance is added to it, after the operation is completed the combined preparation is called a solution. If fully charged with the dissolved substance so that it will retain no more, it is known as a saturated solution. One liquid may be dissolved in another, or a gas may be dissolved in a liquid. The solution of solids

is greatly facilitated by pulverization and by stirring the menstruum. Heat generally aids solution, most substances being more soluble in hot liquids than in cold ones. A saturated solution of one substance may still be capable of dissolving others. Rapid solution of solids without chemical change causes reduction of temperature, while chemical solution produces elevated temperature. Circulatory Solution is performed by suspending the substance to be dissolved near the surface of the solvent in a gauze bag or on a porous shelf. The portion first acted on descends and produces a circulatory movement in the fluid, facilitating the solution of the whole. SOLVENTS employed are chiefly Water, Alcohol, Glycerin, Acids and Oils. Others less frequently used are Ether, Chloroform, Benzin and Carbon Disulphide.

Washing is a simple mechanical process for separating soluble from insoluble matter, by pouring upon it a liquid which will dissolve the soluble portion. Various methods of doing this are in vogue and are often dignified with very high-sounding terms, as Lotion, Affusion, Ablution, An ordinary wash-bottle, with the two glass tubes perforating the cork, is a convenient implement for directing a continuous stream upon a precipitate, while for continuous washing a combination of bottles with a funnel may be used.

etc.

Decantation is the pouring or drawing off a supernatant liquid into another vessel. If done by pouring, a guiding-rod for the liquid to run on is an effective adjuvant; if by drawing, the siphon in some form is usually employed.

Colation, or Straining is another very simple operation, so familiar to every one of ordinary experience as to be scarcely worth describing. The strainers are made of cotton flannel, fine muslin, gauze, woolen felt and other fabrics.

Filtration is a process of straining through a medium so fine as to deliver the filtrate in transparent condition. The filters are made of paper usually, though charcoal, asbestos, sand and other articles are sometimes. employed, and are supported in a funnel of glass or other material held by the ring of a retort-stand. The best filtering-paper is made in Sweden by Munktell, and is white; but a good paper for ordinary use is the "Prat Dumas White," which should always be employed for filtering alkaline or alkaloidal solutions. The gray French papers answer well enough for fluid extracts, tinctures or colored liquids, but should never be used for solutions containing free alkali.

Filtering-paper is folded by doubling a sheet upon itself, and then folding it again directly in the middle. When opened four distinct sections appear, one of which is separated from the other three, and the filter thus formed is placed in a funnel. This arrangement is known as a plain filter, which by repeated creasing is converted into the plaited filter; the latter being the form generally used in pharmaceutical operations

of small extent. In large laboratories special processes of filtration are employed with apparatus of more or less complexity for hot filtration, rapid filtration, etc.

Clarification is the separation from liquids of solid matter, which prevents their being transparent, without using filters or strainers. It may be effected by heat (as in the case of Mel Despumatum), by adding a lighter liquid, by adding albumen, gelatin, milk, or paper-pulp, by fermentation, or by subsidence of the particles in the form of a sediment through long standing.

Decoloration, or the removal of coloring-matter from liquids or from solids in solution, is effected by the use of animal charcoal, which in small operations may be arranged in a funnel or a percolator, and the liquid placed thereon. It should not be forgotten that charcoal absorbs many other principles besides coloring-matter, especially alkaloids, bitters, and astringents, so, that the process of decoloration may be one of serious injury to the efficiency of the preparation.

Separation of liquids which do not mix with each other is a simple mechanical process performed with pipettes of various forms, or with funnels having stop-cocks in their necks. Special forms of receivers are used for the separation of volatile oils from the water which may accompany them during distillation.

Precipitation is the process of separating solids from their solutions, and is usually effected by chemical reaction, though it may be accomplished by other methods, as by adding a second liquid in which the substance is insoluble, by heating albuminous solutions, or by exposing solutions of silver salts to the action of light. The most familiar example of chemical precipitation is the addition of a solution of Mercuric Chloride to one of Potassium Iodide, the result being a double decomposition of the salts and the formation of Mercuric Iodide, which falls to the bottom of the vessel as a brilliant, red, insoluble and crystalline powder. The precipitate is the separated substance, which is usually thrown down, but it remains suspended in some cases, and in others it rises to the top. The precipitant is the substance which is added to produce the precipitation. A magma is a thick, tenacious precipitant remaining behind. after the supernatant liquid is removed by decantation or otherwise. Precipitates are termed flocculent, gelatinous, curdy, granular, crystalline, etc., according to the forms assumed. In small operations they are usually collected on plain filters, and washed by the repeated addition of water.

Crystallization is the process which bodies undergo in passing from the liquid or the gaseous state to the geometrical forms called crystals. Six systems of crystals are recognized by crystallography, which has assumed the dignity of a separate science. Bodies which are not capable